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First, and only for the constructor of the most derived class as described below, virtual base classes shall be initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where “left-to-right” is the order of appearance of the base class names in the derived class base-specifier-list.
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Then, direct base classes shall be initialized in declaration order as they appear in the base-specifier-list (regardless of the order of the mem-initializers).
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Then, non-static data members shall be initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).
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Finally, the compound-statement of the constructor body is executed. [ Note: the declaration order is mandated to ensure that base and member subobjects are destroyed in the reverse order of initialization. —end note ]